Method of regulating molecular weight distribution of polyether glycol

ABSTRACT

A method for controlling the molecular weight distribution of polyether glycol in producing polyether glycol having a specified number average molecular weight by polymerizing tetrahydrofuran as a starting monomer with the use of a heteropoly-acid as a catalyst, which method comprises conducting the polymerization in the presence of an amount of water which can form two phases of the organic phase and a catalyst phase, sampling the polymerization product during the polymerization to determine the molecular weight distribution and, when the molecular weight distribution thus found is narrower than the specified molecular weight distribution, making the residence time distribution of the starting monomer in the catalyst phase wider, while, when the found molecular weight distribution is wider than the specified molecular weight distribution, making the residence time distribution of the starting monomer in the catalyst phase narrower.

This application is a 371 of PCT /JP99/02603, filed May 19, 1999, nowWO99/61507 published Dec. 2, 1999.

TECHNICAL FIELD

The present invention relates to a method for controlling the molecularweight distribution of polyether glycol obtained in producing polyetherglycol by ring-opening polymerization of tetrahydrofuran (hereinafterreferred to as THF) as a starting monomer, using a heteropoly-acid as acatalyst.

BACKGROUND ART

Polyether glycol is an industrially useful polymer as the main rawmaterial of polyurethanes used for polyurethane elastic fiber andsynthetic leather, an additive for oil and a softening agent. Polyetherglycol is required, in its industrial usage, to have an optimummolecular weight and optimum molecular weight distribution according tothe intended uses.

U.S. Pat. Nos. 4,568,775, 4,568,065 and 5,416,240 disclose thatheteropoly-acids can be used as a polymerization catalyst in producingpolyether glycol. These prior art references disclose the activity ofheteropoly-acids as a catalyst. JP-A-5-70585 discloses a method ofcontrolling the average molecular weight of polyoxyalkylene glycol andthe derivatives thereof by using a heteropoly-acid as a catalyst.However, none of these prior art references disclose a method forcontrolling the molecular weight distribution of the polyether glycolobtained.

One of the known methods for obtaining polyether glycol having anoptimum narrow molecular weight distribution which can meet the variousintended uses is, as disclosed in U.S. Pat. No. 5,053,553, a methodwherein polytetramethylene-ether glycol (hereinafter referred to asPTMG) obtained by polymerization is subjected to liquid-liquidextraction using methanol, water and a specific nonpolar solvent toseparate a solvent phase of the upper layer containing PTMG having anarrow molecular weight distribution, thereby to obtain PTMG having anarrow molecular weight distribution. In this method, however, inaddition to the step of polymerization of polyether glycol, anextraction step and further a recovery step must be conducted; moreover,since an organic solvent is used, the cost for its recovery etc. must beadded, leading to economical disadvantage.

Though polyether glycol is sometimes used independently as an additiveand the like, it is mostly used as a reaction starting material.Therefore, a specified number average molecular weight and a specifiedmolecular weight distribution are required according to intended uses.

In particular, when polyether glycol is used as the raw material forelastic fiber typically represented by polyurethane fiber, since themolecular weight distribution of polyether glycol exerts an influence onthe elastic function, particularly on the recovery, of elastic fiber, aprocess for producing polyether glycol is awaited which can control themolecular weight distribution as desired.

The process for producing polyether glycol using a heteropoly-acid as acatalyst is attracting much attention, because it allows the presence ofwater in the reaction system and makes it possible to conductpolymerization in one stage reaction. In particular, in the productionof polyether glycol using this catalyst, a process is eagerly desiredwhich can precisely control the molecular weight distribution of thepolymer.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide, in producingpolyether glycol by using a heteropoly-acid as a catalyst, a methodwhich can efficiently adjust the molecular weight distribution of thepolyether glycol obtained to a specified value or into a specifiedrange.

The present invention provides a method for controlling the molecularweight distribution of polyether glycol obtained which comprises, in aTHF polymerization reaction system using a heteropoly-acid as acatalyst, making an amount of water which can form two phases, namely anorganic phase (THF phase) and a catalyst phase, present in the reactionsystem, and controlling the residence time distribution of the startingmonomer in the catalyst phase in the reaction vessel, thereby to controlthe molecular weight distribution of the polyether glycol obtained.namely a organic phase (THF place) and a catalyst phase, present in thereaction system, and controlling the residence time distribution of thestarting monomer in the catalyst phase in the reaction vessel, therebyto control the molecular weight distribution of the polyether glycolobtained.

It is disclosed in JP-A-59-221326 that the amount of water coordinatedto a heteropoly-acid influences the catalytic activity, and the amountof water coordinated to a heteropoly-acid and the number averagemolecular weight obtained by polymerizing THF are correlated to eachother. However, though the above document describes that the molecularweight distribution of the polyether diol obtained is sharp, itdescribes nothing about the control of molecular weight distribution.

The present inventors have made extensive study on controlling themolecular weight distribution of polyether glycol obtained bypolymerizing THF with maintaining the number of coordinated water ofcatalyst in the reaction system constant. As a result, it has been foundout that the molecular weight distribution of polyether glycol can beprecisely controlled without substantially changing its number averagemolecular weight by keeping the feed amount of the starting monomer THFrelative to the catalyst phase approximately constant in the reactionvessel and controlling the residence time distribution of the startingmonomer which reacts in the catalyst phase. The present invention hasbeen accomplished on the basis of the above finding.

According to the present invention, there is provided a method forcontrolling the molecular weight distribution of polyether glycolobtained in producing polyether glycol having a specified number averagemolecular weight by polymerizing THF as a starting monomer with the useof a heteropoly-acid as a catalyst, which method comprises conductingthe polymerization in the presence of an amount of water which can formtwo phases of the organic phase and the catalyst phase, sampling thepolymerization product during the polymerization to determine themolecular weight distribution and, when the molecular weightdistribution thus found is narrower than the specified molecular weightdistribution, making the residence time distribution of the startingmonomer in the catalyst phase wider, while, when the found molecularweight distribution is wider than the specified molecular weightdistribution, making the residence time distribution of the startingmonomer in the catalyst phase narrower.

According to the present invention, there is further provided a processfor producing polyether glycol having a specified number averagemolecular weight and a specified molecular weight distribution bypolymerizing tetrahydrofuran as a starting monomer with the use of aheteropoly-acid as a catalyst, which process comprises conducting thepolymerization in the presence of an amount of water which can form twophases of the organic phase and the catalyst phase, sampling thepolymerization product during the polymerization to determine themolecular weight distribution and, when the molecular weightdistribution thus found is narrower than the specified molecular weightdistribution, making the residence time distribution of the startingmonomer in the catalyst phase wider, while, when the found molecularweight distribution is wider than the specified molecular weightdistribution, making the residence time distribution of the startingmonomer in the catalyst phase narrower.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a schematic view showing one example of a continuouspolymerization apparatus used in the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the polymerization of THF using a hetropoly-acid as a catalyst, thereaction system forms an emulsion solution wherein two phases, namely aorganic phase containing the polymer and a catalyst phase, aredispersing in the form of liquid droplets.

The polymerization is considered to proceed in the catalyst phase. It isconsidered that along with the progress of polymerization, polyetherglycol dissolving in the catalyst phase is distributed between thecatalyst phase and the organic phase and, under the reaction conditions,the distribution is in a stationary state.

In obtaining polyether glycol having a specified number averagemolecular weight, the molecular weight distribution of the polyetherglycol formed can be controlled by controlling the residence timedistribution of the starting monomer in the catalyst phase.

It is considered that, the polyether glycol formed in the catalyst phasevaries its degree of polymerization according to the residence time ofthe starting monomer in the catalyst phase, but the polymerizationproceeds as an equilibrium reaction. Since the polymer formed in thecatalyst phase is distributed to the organic phase, the molecular weightdistribution of the polyether glycol finally obtained reflects themolecular weight distribution of polyether glycol in the catalyst phase.

Accordingly, by controlling the distribution of the residence times inthe catalyst phase of individual molecules of the starting monomer inthe reaction system, the molecular weight distribution of the polymerobtained can be controlled.

The residence time distribution of the starting monomer in the catalystphase can be controlled, for example, by controlling the contact areaand the contact time between the catalyst phase and the organic phase.

Thus, in order to widen the molecular weight distribution of thepolymer, the residence time distribution in the catalyst phase of thestarting monomer polymerizing in the catalyst phase is widened, while,in order to narrow the molecular weight distribution, the residence timedistribution of the starting monomer in the catalyst phase is narrowed;in this manner, the molecular weight distribution can be controlled.

Preferred methods for controlling the residence time distribution of thestarting monomer in the catalyst phase include the following methods:

(1) The residence time distribution of the starting monomer in thecatalyst phase is controlled by varying the residence time of THF in thereaction vessel (V/F, wherein V is the total liquid volume in thereaction vessel and F is the monomer feed rate to the reaction vessel);when the molecular weight distribution of the polymer is to be widened,the residence time (V/F) is increased, and when the molecular weightdistribution is to be narrowed, the residence time (V/F) is decreased;or

(2) A reaction vessel equipped with a stirrer is used, and the residencetime distribution of the starting monomer in the catalyst phase iscontrolled by varying the stirring power per unit reaction liquid volume(P/V, wherein P is the stirring power and V is the total liquid volume);when the molecular weight distribution of the polymer formed is to bewidened, the stirring power (P/V) is decreased, and when the molecularweight distribution is to be narrowed, the stirring power (P/V) isincreased.

In the former method (1), the average residence time of THF in thereaction vessel varies with changes in V/F.

In order to control the molecular weight distribution of the polyetherglycol without changing its number average molecular weight, it isnecessary to keep the reaction time constant. It has been found,surprisingly, that this can be achieved by keeping the average residencetime of THF per unit amount of catalyst constant.

It is considered that the substantial reaction time is kept constant bycontrolling the amount of catalyst in the reaction vessel. As a result,the molecular weight distribution of the polyether glycol formed can bevaried while keeping its number average molecular weight constant.

The working mechanism in controlling molecular weight distribution byvarying V/F can be considered as follows.

In a continuous reaction, when V/F is varied, the average residence timeof the starting monomer in the reaction vessel changes. At this time, itis considered that when the average residence time is long, theresidence time distribution in the catalyst phase of the startingmonomer in the reaction vessel becomes wide; conversely, when theaverage residence time is short, the residence time distribution in thecatalyst phase of the starting monomer in the reaction vessel becomesnarrow.

That is to say, when V/F is increased, the residence time distributionin the catalyst phase of the starting monomer in the reaction vesselbecomes wider and hence the molecular weight distribution of thepolyether glycol obtained is widened. Conversely, when V/F is decreased,the residence time distribution in the catalyst phase of the startingmonomer in the reaction vessel becomes narrow and hence the molecularweight distribution of the polyether glycol obtained is narrowed.

Thus, the molecular weight distribution of the polyether glycol formedcan be controlled by controlling V/F in the continuous reaction.

In the latter method (2), it is considered that by varying the stirringpower (P/V), the average particle diameters of the liquid droplets ofthe catalyst phase or of the organic phase in the reaction vessel vary,so that the contact area between two phases changes and the frequency ofcoalescence-division of liquid droplets also changes, and consequentlythe amount of mass transfer between the respective phases changes.Accordingly, by varying the stirring power (P/V), the residence timedistribution in the catalyst phase of the starting monomer can becontrolled and hence the molecular weight distribution of the polyetherglycol obtained can be controlled.

When the stirring power (P/V) is increased, the average particlediameters of the liquid droplets formed by the catalyst phase and theorganic phase decrease. Accordingly, the contact area of the two phasesincreases and, at the same time, the frequency of thecoalescence-division of liquid droplets increases. Consequently, theamount of mass transfer between the catalyst phase and the organic phaseincreases, and hence the residence time of the starting monomer in thecatalyst phase becomes more uniform, in other words, the residence timedistribution of the starting monomer in the catalyst phase becomesnarrower. As a result, the molecular weight distribution of thepolyether glycol obtained becomes narrow.

On the contrary, when the stirring power (P/V) is decreased, the contactarea of the catalyst phase with the organic phase decreases and, at thesame time, the frequency of the coalescence-division of liquid dropletsdecreases. Consequently, the residence time distribution of the startingmonomer in the catalyst phase becomes wider, and hence polyether glycolhaving wider molecular weight distribution is obtained.

Accordingly, by using a reaction vessel fitted with a stirrer andcontrolling the stirring power per unit reaction volume (P/V), themolecular weight distribution of the polyether glycol obtained can becontrolled while keeping its number average molecular weight constant.

It is considered that the concept of the present invention can be alsoapplied when a reaction vessel which permits mixing without usingstirring power, such as a line mixer, is used. In such a case, it isconsidered that the molecular weight distribution of the polyetherglycol obtained can be controlled by controlling the particle diametersof liquid droplets of the catalyst phase or the starting monomer phasein the reaction liquid by such a method as changing the flow rate in thereactor.

The method of controlling the molecular weight distribution of polyetherglycol by controlling the THF residence time in the reaction vessel(V/F) and the method of controlling the molecular weight distribution ofpolyether glycol by controlling the stirring power per unit volume (P/V)as described above may also be used in combination.

A preferred embodiment of the present invention is a method forcontrolling the molecular weight distribution of polyether glycolobtained in producing polyethylene glycol having a specified numberaverage molecular weight by polymerizing THF as a starting monomer withthe use of a heteropoly-acid as a catalyst which method comprises:

(a) the step of obtaining, under reaction conditions for obtaining apolymer product having a specified number average molecular weight, acalibration curve which shows the relationship between the residencetime, V/F (when V is the total liquid volume in the reaction vessel andF is the monomer feed rate to the reaction vessel), and/or the stirringpower per unit reaction liquid volume in using a reaction vessel with astirrer, P/V, (wherein P is the stirring power and V is the total liquidvolume in the reaction vessel), and the molecular weight distribution,

(b) conducting the polymerization in the presence of an amount of waterwhich can form two phases of a organic phase and a catalyst phase,sampling the reaction liquid from the polymerization reactor during thepolymerization to determine the number average molecular weight of thepolymerization product and, when the number average molecular weightdetermined deviates from the specified value, modifying the reactionconditions to adjust the number average molecular weight to thespecified value,

(c) the step of determining the molecular weight distribution of thepolymerization product which has reached the specified number averagemolecular weight, and

(d) when the molecular weight distribution determined in the above step(c) differs from the specified value, collating the determined molecularweight distribution with the calibration curve obtained in the step (a)and adjusting the residence time and/or the stirring power to thevalue(s) corresponding to the specified molecular weight distribution.

The above-mentioned steps (a) to (d) are explained below.

Step (a): The relation(s) between the molecular weight distribution ofpolyether glycol having a specified number average molecular weight andP/V and/or V/F are (is) determined as an empirical formula. The range ofthe error of the specified number average molecular weight, which maydepend on the intended use of the polyether glycol, is usually not morethan ±100, preferably ±50 and, when the polyether glycol is to be usedfor example as a reaction starting material, more preferably not morethan ±30.

When, for example, a PTMG having a number average molecular weight of1800 is to be produced by using a heteropoly-acid as the catalyst, thefollowing relational expressions of formula (I) and formula (II) can beexperimentally determined. In the formulas, Mw/Mn _is the ratio of theweight average molecular weight (Mw) to the number average molecularweight (Mn) of the PTMG, obtained by using GPC, and is an index ofmolecular weight distribution.

Mw/Mn=K·(P/V)⁶⁰  (I)

wherein K and α are constants which can be determined experimentally.

Mw/Mn=K′·(V/F)⁶²  (II)

wherein K′ and β′ are constants which can be determined experimentally.

Step (b): In the presence of an amount of water which can form twophases of a organic phase and a catalyst phase, the polymerizationreaction is conducted under conditions under which polyether glycolhaving the specified number average molecular weight will be obtained,and the number average molecular weight of the polymer obtained ismeasured. When the number average molecular weight thus measured doesnot agree with the specified value, adjustment is made so as to attainthe specified value by using known methods, for example, the control ofthe amount of coordinated water of the heteropoly-acid catalyst, thecontrol of the reaction temperature, and the like.

Step (c): The molecular weight distribution (Mw/Mn) of the polyetherglycol having the specified number average molecular weight isdetermined by means of GPC.

Step (d): When Mw/Mn determined by the above step (c) deviates from thespecified value (desired value), the molecular weight distribution ofPTMG is controlled by varying the residence time (V/F) and/or thestirring power (P/V) on the basis of the calibration curve obtained inthe step (a).

Preferably, the steps (b) to (d) are repeated until a polymer having thespecified molecular weight distribution Is obtained at the specifiednumber average molecular weight.

In the present invention, the THF residence time V/F in the reactionsystem is, for controlling the molecular weight distribution ofpolyether glycol, preferably 0.5-20 hours, more preferably 0.7-15 hours.For obtaining polyether glycol having the specified number averagemolecular weight, when V/F is decreased, the conversion in reactiondecreases and reaction efficiency decreases; when V/F is increased, thereaction time lengthens. Therefore, it is preferable to select V/F fromthe above mentioned range.

The stirring power P/V in the reaction system is, for controlling themolecular weight distribution of polyether glycol, preferably 0.2-6.0kW/m³, more preferably 0.75-4.5 kW/m³. When P/V is less than 0.2 kW/m³Wthe stirring is insufficient, resultantly the distribution of liquiddroplet particle diameter in the reaction system becomes wide and thecontrol of the molecular weight distribution becomes difficult. On theother hand, when P/V exceeds 6.0 kW/m³, the stirring efficiency changesno more even when a larger power is applied and also the molecularweight distribution of the polyether glycol obtained does not change.

After completion of the polymerization reaction, the monomer is removedby distillation or the like, from the phase which comprises mainlymonomer and older and is obtained by phase separation, to recoverpolyether glycol.

In the present invention, the production of polyether glycol can beeffected, besides by homopolymerization of THF, by using as a comonomercyclic ethers or diols which are copolymerizable with THF. Thecomonomers may be, for example, oxetane and oxetane derivatives, e.g.,3,3-dimethyloxetane, cyclic ethers such as methyltetrahydrofuran,1,3-dioxolan and tetrahydropyran, ethylene glycol, propylene glycol,1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol,neopentyl glycol, diethylene glycol, dipropylene glycol and the like.

The “heteropoly-acid” used in the present invention is the generic nameof oxyacids formed by the combination of the oxide of at least oneelement selected from the group consisting of Mo, W and V with anoxyacid containing another element, e.g., P, Si, As, and Ge. The atomicratio of the former element(s) to the latter element(s) is preferably2.5-12.

Specific examples of heteropoly-acids include phosphomolybdic acid,phosphotungstic acid, phosphomolybdotungstic acid, phosphomolybdovanadicacid, phosphomolybdotungstovanadic acid, phosphotungstovanadic acid,phosphomolybdoniobic acid, silicotungstic acid, silicomolybdic acid,silicomolybdotungstic acid, silicomolybdotungstovanadic acid,germanotungstic acid, arsenomolybadic acid and arsenotungstic acid.

Though the amount of the heteropoly-acid used is not particularlylimited, when the amount of the heteropoly-acid in the reaction systemis small the polymerization velocity tends to be low. The amount of theheteropoly-acid relative to the monomer is preferably 0.1-20 times byweight, more preferably 0.5-5 times by weight.

When the polymerization temperature is high, the degree ofpolymerization tends to be low owing to depolymerization of the polymertaking place. Therefore, the polymerization temperature is 0-150° C.,preferably 30-80° C.

Since the polymerization reaction can be conducted while the monomer andthe heteropoly-acid are being mixed, the reaction does not particularlyrequire the use of a solvent, but, if desired, an inert solvent to thereaction may be added.

The present invention is described in detail below with reference toExamples, but the invention is in no way limited thereto.

EXAMPLE 1

The following polymerization was carried out by using the continuouspolymerization apparatus shown in FIG. 1. First, in the 500-ml reactor 1having a stirring device and a reflux cooler was placed as a catalyst110 ml of a solution of a specific gravity 2.1 obtained by dissolvingsilico-tungstic acid together with a small amount of water in THF, then310 ml of THF (monomer) was added thereto, and the resulting mixture wasstirred. The temperature of the reactor was set at 60° C., and themonomer was fed at a rate of 70 ml/h to the reactor 1. The reactionliquid was circulated between the reactor and the phase separationvessel 2, and the upper layer resulting from phase separation waswithdrawn at the same rate as the monomer feed rate. During thereaction, the amount of water fed from the water feed vessel 3 to thereactor 1 was controlled so that the amount of water includingcoordinated water in the catalyst phase in the reactor 1 might be keptconstant. The liquid withdrawn from the phase separation vessel 2 wasfed to the distillation column 4 and the unreacted monomer was removed,to obtain polyether glycol (PTMG).

After about 10 hours of continuous operation, the number averagemolecular weight (Mn) and the molecular weight distribution (Mw/Mn) ofPTMG at the stationary state were found to be 2,000 and 1.8,respectively.

To obtain a PTMG having a narrow molecular weight distribution, 45 ml ofthe silicotungstic acid catalyst solution was additionally supplied andthe feed rate of THF was changed to 100 ml/hr without changing theliquid volume of the reactor 1. The value of V/F in the reactiondecreased from 6.0 to 4.2. During the time, the stirring power per unitreaction liquid volume (P/V) was fixed at 2.0 kW/m^(3.)

The PTMG obtained had an Mn of 2,000 and an Mw/Mn of 1.6. Thus, themolecular weight distribution could be narrowed without change in thenumber average molecular weight by decreasing V/F.

The number average molecular weight and the molecular weightdistribution (weight average molecular weight/number average molecularweight) were determined by using gel permeation chromatography (GPC).

EXAMPLE 2

The same procedures as in Example 1 were followed except that thecatalyst used was 50 ml of a phosphomolybdic acid solution adjusted to aspecific gravity of 1.80, the initial charge of THF was 370 ml, V/F was4 hours, stirring power (P/V) was 2.2 kW/m³.

The PTMG obtained had an Mn of 1500 and an Mw/Mn of 1.6.

To obtain a PTMG having a wide molecular weight distribution, thecatalyst volume was changed to 30 ml and V/F to 6.46 hours. As theresult, a PTMG having an Mn of 1505 and an Mw/Mn of 1.8 was obtained.

EXAMPLE 3

The same procedures as in Example 2 were followed except that 140 ml ofphosphomolybdic acid was used as the catalyst, V/F was changed to 4hours and P/V was changed to 2.1 kW/m³, to obtain a PTMG having an Mn of1500 and an Mw /Mn of 1.65.

Further, to obtain a PTMG having a wider molecular weight distribution,the stirring power (P/V) was reduced to 1.2 while other conditions werekept unchanged, to obtain a PTMG having an Mw/Mn of 1.90. The PTMG hadan approximately the same Mn of 1505.

EXAMPLE 4

Polymerization of THF was carried out according to the same procedure asin Example 1 except that phosphotungstic acid was used as a catalystsolution of a specific gravity of 2.05 and the reaction liquid volume Vin the reactor 1 was kept constant at 420 ml. First, in order to findthe relation between Mw/Mn and V/F, with P/V fixed at 1.9 kW/m³, the Mnand the Mw/Mn of PTMG obtained under conditions 1 to 3 shown in Table 1were measured. The results obtained are shown in Table 1.

Next, in order to find the relation between Mw/Mn and P/V, with V/Ffixed at 4 hours, the Mn and the Mn/Mw of PTMG obtained under conditions4 to 6 shown in Table 2 were measured. The results obtained are shown inTable 2.

From the results shown in Table 1 and Table 2, the following relations(1) and (2) were obtained.

Mw/Mn=1.46×(V/F)^(0.134)  (1)

Mw/Mn=1.95×(P/V)^(−0.141)  (2)

In the operation of the condition (1), Mn was 1750 and Mw/Mn was 1.7.When the molecular weight distribution (Mw/Mn) is to be reduced to about1.6, the appropriate value of V/F is expected, from the formula (1), tobe about 2.0 hours. Accordingly, the amount of the catalyst was set at180 ml, the THF feed rate was set at 210 ml/hr, and the withdrawing rateof the upper phase of the phase separation vessel 2 was also set at 210ml/hr. The PTMG obtained had an Mw/Mn of 1.6 and an Mn of 1750.

TABLE 1 Reaction vessel Number total liquid THF feed average Molecularamount rate Catalyst molecular weight V F V/F *) amount weightdistribution Condition Heteropoly-acid (ml) (ml/hr) (hr) (ml) Mn Mw/Mn 1Phosphotungstic 420 140 3.0 120 1750 1.7 acid 2 Phosphotungstic 420 854.95 75 1745 1.8 acid 3 Phosphotungstic 420 60 7.0 50 1755 1.9 acidNote: *) The amount of catalyst solution obtained by dissolvingheteropoly-acid in THF in the presence of a very small amount of waterand adjusting the liquid specific gravity by the amount of water added.

TABLE 2 Reaction vessel total Reaction Number liquid vessel averageMolecular amount stirring molecular weight V power P/V weightdistribution Condition Heteropoly-acid (ml) (mW) (kW/m³) Mn Mw/Mn 4Phosphotungstic 420 462 1.1 1750 1.90 acid 5 Phosphotungstic 420 756 1.81745 1.82 acid 6 Phosphotungstic 420 1092 2.6 1755 1.7 acid

EXAMPLE 5

The conditions 6 of Example 4 were changed in order to narrow themolecular weight distribution. To obtain a PTMG having an Mw/Mn of 1.6,P/V was set at 4.2 on the basis of the calibration curve of the formula(2) of Example 4. The stirring power of the reactor 1 was increased to1765 mW, and polymerization reaction was continued.

The PTMG obtained had an Mw/Mn of 1.58 and an Mn of 1750. Thus, a PTMGhaving an approximately desired molecular weight distribution wasobtained.

Industrial Applicability

According to the method of the present invention, polyether glycolswhich have a specified molecular weight and specified molecular weightdistribution can be produced to meet intended uses.

What is claimed is:
 1. A method for controlling the molecular weightdistribution of polyether glycol obtained in producing polyether glycolhaving a specified number average molecular weight by polymerizingtetrahydrofuran as a starting monomer with the use of a heteropoly-acidas a catalyst, without substantially changing the average molecularweight which method comprises conducting the polymerization in thepresence of an amount of water which can form two phases of an organicphase and a catalyst phase, sampling the polymerization product duringthe polymerization to determine the molecular weight distribution and,when the molecular weight distribution thus found is narrower than thespecified molecular weight distribution, making the residence timedistribution of the starting monomer in the catalyst phase greater,while, when the found molecular weight distribution is wider than thespecified molecular weight distribution, making the residence timedistribution of the starting monomer in the catalyst phase less, whereinthe residence time distribution in the catalyst phase of the startingmonomer is controlled by varying the tetrahydrofuran residence time inthe reaction vessel V/F, wherein V is the total liquid volume in thereaction vessel and F is the rate of monomer feed to the reactionvessel, V/F being increased when the molecular weight distribution ofthe polymer is to be widened, while V/F being decreased when themolecular weight distribution is to be narrowed.
 2. A method forcontrolling the molecular weight distribution of polyether glycolobtained in producing polyether glycol having a specified number averagemolecular weight by polymerizing tetrahydrofuran as a starting monomerwith the use of a heteropoly-acid as a catalyst, without substantiallychanging the average molecular weight which method comprises conductingthe polymerization in the presence of an amount of water which can formtwo phases of an organic phase and a catalyst phase, sampling thepolymerization product during the polymerization to determine themolecular weight distribution and, when the molecular weightdistribution thus found is narrower than the specified molecular weightdistribution, making the residence time distribution of the startingmonomer in the catalyst phase greater, while, when the found molecularweight distribution is wider than the specified molecular weightdistribution, making the residence time distribution of the startingmonomer in the catalyst phase less, wherein the residence timedistribution in the catalyst phase of the starting monomer is controlledby using a reaction vessel with a stirrer and varying the stirring powerper unit reaction liquid volume P/V, wherein P is the stirring power andV is the total liquid volume in the reaction vessel, P/V, beingdecreased when the molecular weight distribution of the polymer is to bewidened, while P/V being increased when the molecular weightdistribution of the polymer is to be narrowed.
 3. A method forcontrolling the molecular weight distribution of polyether glycol inproducing polyether glycol having a specified number average molecularweight by polymerizing tetrahydrofuran with the use of a heteropoly-acidas a catalyst, which method comprises (a) the step of obtaining, underreaction conditions for obtaining a polymer product having a specifiednumber average molecular weight, a calibration curve which shows therelationship between the residence time, V/F, wherein V is the totalliquid volume in the reaction vessel and F is the rate of monomer feedto the reaction vessel, and/or the stirring power per unit reactionliquid volume in using a reaction vessel with a stirrer, P/V, wherein Pis the stirring power and V is the total liquid volume in the reactionvessel, and the molecular weight distribution, (b) the step ofconducting the polymerization in the presence of an amount of waterwhich can form two phases of an organic phase and a catalyst phase,sampling the reaction liquid from the polymerization reactor during thepolymerization to determine the number average molecular weight of thepolymerization product and, when the number average molecular weightdetermined deviates from the specified value, modifying the reactionconditions to adjust the number average molecular weight to thespecified value, (c) the step of determining the molecular weightdistribution of the polymerization product which has reached thespecified number average molecular weight, and (d) the step ofcollating, when the molecular weight distribution determined in theabove step (c) differs from the specified value, the determinedmolecular weight distribution with the calibration curve obtained in thestep (a) and adjusting the residence time and/or the stirring power tothe value(s) corresponding to the specified molecular weightdistribution.
 4. The method according to claim 3, which comprisessampling the polymerization,product appropriately during thepolymerization and repeating the steps (b) to (d).
 5. A process forproducing polyether glycol having a specified number average molecularweight and a specified molecular weight distribution by polymerizingtetrahydrofuran with the use of a heteropoly-acid as a catalyst, whichprocess comprises (a) the step of obtaining, under reaction conditionsfor obtaining a polymer product having a specified number averagemolecular weight, a calibration curve which shows the relationshipbetween the residence time, V/F, wherein V is the total liquid volume inthe reaction vessel and F is the rate of monomer feed to the reactionvessel, and/or the stirring power per unit reaction liquid volume inusing a reaction vessel fitted with a stirrer, P/V, wherein P is thestirring power and V is the total liquid volume in the reaction vessel,and the molecular weight distribution, (b) the step of conducting thepolymerization in the presence of an amount of water which can form twophases of an organic phase and a catalyst phase, sampling the reactionliquid from the polymerization reactor during the polymerization todetermine the number average molecular weight of the polymerizationproduct and, when the number average molecular weight determineddeviates from the specified value, modifying the reaction conditions toadjust the number average molecular weight to the specified value, (c)the step of determining the molecular weight distribution of thepolymerization product which has reacted the specified number averagemolecular weight, and (d) the step of collating, when the molecularweight distribution determined in the above step (c) differs from thespecified value, the determined molecular weight distribution with thecalibration curve obtained in the step (a) and adjusting the residencetime and/or the stirring power to the value(s) corresponding to thespecified molecular weight distribution.